Water Temperature for Hydrostatic Test 1

[PAN]

Should we control the water temperature during hydrostatic test? In my case, the MDMT is 9.9 degree C.

Can I perform the hydrostatic test with water at lower temperature? Please comment.

 

[GenB]

the water temp should be between 70-120F,
water purity is needed on alloy steels.
genb

 

[metengr]

PAN;
What is the construction code of the vessel? The construction code will dictate the water temperature requirements for hydrostatic testing.

 

[1969grad]

Given sufficient time the water temperature will stabilize to the environmental temperature which is the temperature of the vessel walls. Hence the water will expand or contract depending on the fill temperature and cause the test pressure to rise or fall.

I would not go to the extra expense to control the water temperature but beware that the test pressure will vary until the water temperature stabilizes. In the case of contraction you have to make sure the test pressure does not drop too low.

 

[robsalv]

We have strict guidelines on water temperature during hydro.

For vessels <50mm thick, the minimum hydrotest temperature of the shell shall be 6degC greater than the highest of the CET/MDMT/MAT.

For vessels >50mm thick and greater, the margin is 17degC.

In our Australian plant we have a mix of ASME and AS vessels - hence the range of low temperature references.

AP579 also recommends these margins.

Cheers

Rob

 

[PAN]

metengr,
The construction code for the vessel is ASME Sec. VIII Div. 2. Please advise me the related paragraph.

 

[metengr]

Yes. The applicable reference for hydrostatic testing for a Div 2 vessel is as follows;

ASME Section VIII, Div 2 Article T-3 "Hydrostatic Tests"

AT-352, which states that the temperature of the fluid for hydrostatic testing shall be at least 30 deg F ABOVE the minimum design metal temperature. The maximum temperature shall be less than 120 deg F.

 

[adrianviorel]

Dear Metengr,
The solution you propose is leading to a possible absurd situation.
Let's suppose that material is ASTM A 516 gr. 65 , which is not quite uncommon for pressure vessels, and has a minimum design temperature of -29 C. How can a hydrotest be performed below zero? I think I miss something ;please be so kind to explain.

 

[jte]

adrian-

I'd suggest you re-read metengr's post a bit more slowly. Nothing in the post states that the test shall be below freezing.

To rephrase the post: The water temperature shall be no less than 30°F higher than the MDMT but not to exceed 120°F.

In your example, with a MDMT of -20°F, the water shall be somewhere between 10°F and 120°F. Most reasonable folks would make sure the water temperature stays a few degrees above freezing which would be easily in the required range.

On a related note: Has anyone ever seen a hydrotest turn into an ice test? I imagine that a cold weather hydro left outside overnight with no heaters could cause a bit of damage! For the process engineers: How much pressure would it take to raise the freezing temperature by one degree?

jt

 

[robsalv]

Leave a hydrotest on overnight at your own peril.

The combination of a highish MDMT, pressures exceeding DP and dropping overnight temperatures are a bad recipe.

Cheers

Rob

 

[davefitz]

The hydrotest temperature becomes more problematic as we use more advanced alloys in large boiler.

The newer high temperature creep resistant ferritic alloys ( P91, P92,P112) have very low ductility and low notch toughness at 70 F, and this drops off to near zero toughness below 70F, or if unusual weld electrodes or unacceptable heat treatment was used. Two other items worsen this hydrotest problem.

First, these pipelines have built in stresses , either due to cold springing or lack of effected in-service creep relief of shakedown stresses. So the pipes can be considered to be highly spring loaded, with high stress concentrations at the elbows and at the welds lines to supported valves.

Second, the typical means of filling the unit with hot water from the economizer, thru the drum to the main steam outlet, does not guarantee that the final components( ie, main steam outlet header and Xfer pipe to turbine))will be at a sutiably hot temperature. In particular, if the unit was stored dry and cold in a cold environment, the hydrotest water will probably not be above 70F by the time it reaches and fills the Xfer pipe to teh turbine, and yet it is exactly those final components that have null ductility. To properly hudrotest those unit, one might choose to fill from the outlet to the economizer, and monitor or measuer actual metal temperatures at various locations to ensure no part of the unit is below 70F.